Secondary containment systems have been developed to overcome the environmental problems that have been encountered with respect to leakage of hazardous fluids from tanks and pipe lines. This has been a particular problem with underground installations in which undetected leakage of hazardous fluids into the surrounding terrain over long periods of time without detection has produced harmful conditions and extensive pollution which are difficult and expensive to clean up when they are ultimately found.
The petroleum, chemical, and natural gas industries have long recognized that conventional un-contained underground piping is a major source of leaks and consequent product loss and pollution liability. Conventional underground fluid piping systems are typically made of steel or plastic which include rigid straight lengths of pipe, tee fittings, elbows, connectors, unions, and swing joints or flexible connectors. The assembly of those components creates a fluid piping system with many joints and typically a layout design that has many turns and congested plumbing areas. The primary source of leaks is the joints in the numerous associated fittings which can be effected by ground movement, improper installation and corrosion.
Un-contained conventional underground piping systems, which transmit hazardous fluids, have been responsible for, contamination of ground water, fires and explosions, due to leakage. In response to a public mandate to stop environmental pollution and prevent these safety hazards from occurring, federal, state and local regulatory agencies have implemented strict regulations and building codes for underground piping which transmit hazardous fluids.
Equipment manufacturers have responded by developing and producing a variety of secondary containment systems for conventional underground piping which are designed to contain and prevent any leakage from escaping into the environment. Many of these secondary containment systems have proven to be effective containment but have been found to be of an unexceptable design and difficult and costly to install and service.
One approach to secondary containment of underground conventional piping has been to line the piping trench with a product impervious flexible membrane liner or a semi-rigid trough. The technique can provide a measure of secondary containment of leaking product, but such an approach does not allow for effective leak detection, in that it does not permit determination of which piping line is leaking, the location of the leak in the piping line and when the leak occurred. This type of secondary containment system requires that all contaminated backfill materials contained within the trench be removed after a leak has been repaired. Also, integrity testing of such a secondary containment system, by means of air pressure testing, is not possible. Further, such secondary containment systems, generally, do not provide 360.degree. containment and, therefore, can fill with water, thereby eventually becoming ineffective.
Another approach toward solving the problem of leakage from the underground conventional piping has been to install a larger semi-conventional piping system over the conventional product piping as a means of secondary containment. In such an arrangement, the outer secondary containment rigid pipe is installed simultaneously with the product piping. The outer secondary containment pipe by necessity, has a larger diameter than the product supply pipe to enable the secondary containment pipe to slide over the smaller diameter product supply pipe. The secondary containment pipe fittings are of a clam shell design adapted to fit over the product supply pipe fittings and connect to the secondary containment pipe. The clam shell fitting is sealed to itself and the secondary containment pipe by a variety of sealing techniques. Depending on the type of secondary containment system used these sealing techniques could include metal or plastic fasteners used with a combination of adhesives, sealants and rubber gaskets. Such secondary containment systems are generally, expensive to install, because of the cost of the components which are used and the time required to assemble both the product and secondary containment piping system. In addition, such secondary containment systems, because of their design, do not allow for complete visual inspection of the entire product piping system during its integrity testing. Should a leak occur, it can be determined which product piping line is leaking, but generally cannot identify the location in the product supply pipe the leak has originated. Consequently, the entire length of the particular secondarily contained piping line must be excavated, in order to locate and repair the leak.
Yet, another approach which has been taken toward solving the problem of leakage, in underground conventional product piping, has been to install another type of semi-conventional piping system over the conventional product piping. This secondary containment system differs from the systems described above in a number of ways. The outer secondary containment pipe is not entirely a rigid straight pipe, but rather a combination of a rigid straight pipe with a larger diameter convoluted plastic pipe over it which produces a telescoping effect. The convoluted section of secondary containment pipe serves as a means of containment of the product pipe 90.degree. and 45.degree. fittings, as well as unions, flexible connectors and swing joints, should they be attached. This convoluted pipe is designed to be flexible and sized to be shifted around any angles in the product piping systems. The only fitting required for this type of secondary containment system is a non-split oversized tee fitting which is sized large enough to insert the product piping tee fitting prior to assembly of the product piping. This secondary containment system makes sealed connections by means of rubber gaskets in combination with metal band clamps. Such secondary containment systems are less expensive to install than those previously stated and do allow for complete inspection of the product piping system during integrity testings. Also, this type of secondary containment system can be integrity tested by means of air testing and should a leak occur, it can be determined which product piping line is leaking but generally cannot identify the location in the product pipe the leak has originated. Consequently, the entire length of the particular secondarily contained pipe line must be excavated, in order to locate and repair.
Generally, consideration for both present and future regulatory and user requirements for underground product piping dictate that the piping system possess a number of basic characteristics and meet a number of design, testing and service criteria. Among the basic characteristics and criteria are:
(1) The product piping line should be of such a design that all components from beginning to end be secondarily contained.
(2) Both the product piping and the secondary containment pipe be compatible with the fluids to be transmitted.
(3) The secondary containment system must be made of materials which is non-corrosive, dielectric, non-degradable and resistant to attack from microbial growth found in many soils.
(4) The secondary containment system must be designed and made from a choice of materials which provides sufficient strength to withstand the maximum underground burial loads.
(5) After installation, connection and sealing of the product piping line, the secondary containment system shall permit complete view of the product piping and its associated fittings and components during integrity testing.
(6) The secondary containment system should provide a means of leak detection.
(7) The product piping and its secondary containment system should each provide a means to perform an air pressure and/or hydrostatic integrity test.
(8) Should a leak occur in the product piping, the secondary containment system and/or its leak detecting system should be able to identify the exact location of the leak.
It is the purpose of this invention to address these problems.